The proposed research on serum lipoproteins involves the detailed investigation of the structure, binding properties, and transport function of mammalian (bovine and human) serum high density lipoproteins. Work on the lipoprotein structure will be carried out by three complementary approaches: 1) study of the properties of isolated lipoprotein components in aqueous solutions, 2) stepwise reassociation of lipoprotein components into well defined protein-lipid complexes, and 3) perturbation of intact lipoprotein structure by enzymatic, chemical, and physical means. Fluorescence polarization will be the major technique in structural studies, especially in work on protein association-disassociation behavior and in perturbation studies where strategically placed fluorescent probes may report on the freedom of motion of lipid, protein, or interphase regions of native lipoproteins. and of reassembled complexes. In the area of high density lipoprotein function, possible binding of various ligands will be explored by classical equilibrium dialysis techniques for soluble ligands, and by exposure to lipids dispersed on solid surfaces for lipophilic ligands. Interaction of lipoproteins and reassociated protein-lipid complexes with liposomes and erythrocyte membranes will be observed by the exchange of radioactively labeled lipids and fluorescent labeled proteins between the two types of structures. It is hoped that the experiments on high density lipoprotein function may clarify the obscure role of this class of lipoproteins in blood transport and work on lipoprotein structure should contribute to the understanding of biological membrane structure at the molecular level, and to the elucidation of the process of lipoprotein component deposition in atherosclerotic plaques.